Such pipe joint structures for heat exchangers have hitherto been known in, for example, a patent document 1. Specifically, in a heat exchanger, fins are provided between a plurality of tubes through which refrigerant flows to form a core portion, and a pair of tank portions are disposed on both ends of the plurality of tubes. A socket connected to fluid flow paths on the inlet and outlet sides is disposed in the vicinity of one tank portion, and inlet and outlet pipes for allowing the refrigerant to flow thereto and therefrom are configured to be fixed to the socket.
The core portion, tank portions and socket are integrally formed by connection using brazing in a furnace. After the brazing in the furnace, one-side ends of the inlet and outlet pipes are disposed on an opening side of the socket, and then the inlet and outlet pipes are connected to the socket by torch brazing in another connection step. In other words, the inlet and outlet pipes are fixed to the fluid flow paths on a heat exchanger side via the socket through connection by the torch brazing.
A method for fixing an entrance pipe and a fluid flow path from a heat exchanger is known as disclosed in a patent document 2. In the patent document 2, on the tip side of the pipe, an insertion cylindrical portion and an annular bulge portion protruding in a radial outward direction are formed, and on the tip side of the fluid flow path, first, second and third circumferential surfaces are formed for insertion of the tip of the pipe.
The insertion cylindrical portion is inserted into the first circumferential surface, a seal member for keeping liquid tightness is abutted against the second circumferential surface, and the bulge portion is inserted into the third circumferential surface. The tip of the pipe is inserted into the tip side of the fluid flow path with the seal member disposed on the back of the insertion cylindrical portion. The tip side of the third circumferential surface is plastic-deformed inward to be fixed with the pipe in a state where the pipe is inserted into the fluid flow path.    [Patent Document 1] JP-A-2004-28393    [Patent Document 2] JP-A-2001-280558
As disclosed in the patent document 1, however, performing the torch brazing in another step disadvantageously leads to an increase in processing cost in a connection step in manufacturing of the heat exchanger. In addition, the inlet pipe and the outlet pipe are protruded from the heat exchanger in the transporting of the heat exchanger after the torch brazing. This results in poor transportability of the heat exchanger to an assembly workplace where the heat exchanger is to be assembled to an air conditioning duct, and in deteriorated interim storage capability of the heat exchanger at the assembly workplace.
In order to improve the transportability and the interim storage capability, a method for fixing the heat exchanger by fastening has been proposed as disclosed in the patent document 2. In this case, inlet and outlet pipes, and fluid flow paths on the inlet and outlet sides are separately fixed, thereby leading to an increase in the number of steps of assembly. Furthermore, an adjustment step of adjusting an attachment pitch between the pipes needs to be provided, which disadvantageously results in poor productivity.